The ganzfeld procedure is a mild sensory isolation technique that was first introduced into experimental psychology during the 1930s and subsequently adapted by parapsychologists to test for the existence of psi--anomalous processes of information or energy transfer such as telepathy or other forms of extrasensory perception that are currently unexplained in terms of known physical or biological mechanisms. Parapsychologists developed the ganzfeld procedure, in part, because they had become dissatisfied the card-guessing methods for testing ESP pioneered by J. B. Rhine at Duke University in the 1930s. In particular, they believed that the repetitive forced-choice procedure in which a participant repeatedly attempts to select the correct "target" symbol from a set of fixed-alternatives failed to capture the circumstances that characterize reported instances of psi in everyday life.